This invention relates to an injection molding machine which has a machine bed, a mold closing unit which is supported on the machine bed and which is adapted to selectively receive either a first type of mold assembly having a central injection opening and a central mold cavity and intended for a symmetrical injection (central charging) or a second type of mold assembly having an off-center injection opening and a central cavity and intended for an asymmetrical injection (linear charging). The injection molding machine further has a platform which is supported on the machine bed and which, in turn, supports an injection molding unit that includes a carrier block, as well as a plasticizing cylinder which is received in the carrier block as well and a feed screw which is received in the plasticizing cylinder. There is provided a first drive arrangement which is adapted to axially displace the injection molding unit as well as a second drive arrangement which is adapted to pivot the injection molding unit from a first working position defined by a central injection axis and serving the first type of mold assembly, into another working position in which the second type of mold assembly is served. The injection molding unit is swung in a pivot plane that includes the central injection axis.
In a known injection molding machine, as disclosed in German Gebrauchsmuster (utility patent) 1,852,612, a central mold charging or a linear mold charging of an injection mold assembly may be selectively performed, dependent on whether the mold closing unit holds a mold assembly with a central, or, respectively, a non-central injection opening. For this purpose, the platform on which the injection molding unit is mounted may be pivoted about a stationary horizontal axis. The hydraulic drive cylinder utilized as a drive arrangement for effecting the pivotal motion is supported on the axially fixed platform which forms a pivotal unit with the injection molding unit.
It is further known--as disclosed, for example, in German Gebrauchsmuster 6,942,324 --to pivotally support the injection molding unit of an injection molding machine in such a manner that it may be pivoted out of a position determined by a central injection axis, into two opposite directions for maintenance purposes. The injection molding unit guided on columns is pivotal on a horizontal shaft which is supported in work cylinders that form part of the driving arrangement and which are oriented coaxially with the columns.
Further, as disclosed, for example, in German Offenlegungsschrift (non-examined published application) 2,504,719, an injection molding machine is known whose injection molding unit may be pivoted out of a working position determined by a central injection axis in a predetermined pivotal direction for performing maintenance work thereon. The pivot shaft is, for this purpose, supported in a yoke which may be shifted parallel to the injection axis.
It is further known--as disclosed, for example, in German Offenlegungsschrift 3,630,416--to remove plastic material from the injection molding unit by performing a "blank" injection step, prior to utilizing another plastic material in the plasticizing cylinder. For this purpose, a plate member is positioned in front of the injection opening of the injection mold assembly onto which the residual plastic material is ejected from the plasticizing cylinder in the course of the blank injection.
Frequently, with the change of the type of injection mold assemblies in the injection molding machine (for example, to effect a changeover from a central charging to a linear charging), there is associated a replacement of the plastic material which, in turn, requires a cleaning or replacement of the plasticizing cylinder.